Until recently, the use of chlorofluorocarbons to cool electronic circuitry was universal. However, concern over the hole in the ozone layer has directed attention to substituting other techniques for anything involving CFCs.
In a commonly owned co-pending U.S. patent application Ser. No. 07/835,117 filed on Feb. 14, 1992, there is disclosed the use of direct liquid nitrogen spray as a substitute for liquid CFC spray for testing circuitry. Therein, there is a complete discussion of the environmental and human compatibility of nitrogen vs. that of CFCs, and the effectiveness of liquid nitrogen in removing heat from circuitry.
The nitrogen spray is extremely useful for rapidly cooling specific circuit elements, or small portions of circuitry, but is less effective in trying to cool entire assemblies (which may range from anywhere around 30 cubic inches (about 500 cubic centimeters) to about 300 cubic inches or more (about 5,000 cubic centimeters or more). As described in the aforementioned co-pending application, the most effective manner of cooling is contacting liquid cryogen directly on the surface of the object to be cooled, whereby the heat of vaporization of the cryogen will extract significant heat from the article being cooled as the nitrogen gasifies.